1. Field of the Invention
The present invention relates to a pulley, and more particularly to a pulley which is lightweight and can be produced in a simple manner.
2. Description of Related Art
FIG. 1 illustrates a conventional pulley which acts as a damper pulley. As shown, a cylindrical boss portion 10, to be press-fitted onto a rotary shaft (not shown), and an annular main portion 12, provided outside the cylindrical boss portion 10 are integrally formed by machining a cast metal. A metallic ring body 16, acting as a damper mass, is joined to the outer periphery of the main portion 12 via rubber body 14. V-shaped grooves 18 are formed in the outer periphery of the metallic ring body 16. Thus, the metallic ring body 16 also serves as a belt retaining portion of the pulley.
The pulley formed of cast metal is large in thickness, and accordingly has substantial weight, and also requires machining work, which increases production costs.
FIG. 2 illustrates another conventional pulley. As shown, in order to reduce both the weight and production cost thereof, the main portion 12 and the belt retaining portion 19 are integrally formed from a thin metal plate by press-forming. However, the cylindrical boss portion 10 is formed separately, from a thick metal plate and is coupled to the main portion 12. The boss portion 10 is made thick, since it requires a high strength, as compared to the remaining portions.
The conventional pulley of FIG. 2 requires a troublesome welding process to secure the cylindrical boss portion 10 to the main portion 12, thus increasing production costs. In addition, with this conventional pulley, the weight cannot be sufficiently reduced.